This invention relates generally to combination locks, and more particularly to combination locks of the type employing dial-driven rotary elements, such as sleeves, that must be turned to a predetermined position to open the lock.
Because of their small size and relatively simple construction, combination locks of the type to which the invention pertains are particularly well adapted for use as locking mechanisms on luggage and the like. One type of prior combination lock, disclosed in U.S. Pat. No. 3,800,571 to Heine, issued Apr. 2, 1974, and assigned to the same assignee as the present invention, employs a flat, spring-biased bolt pivoted along one edge and moved to a locked position by sleeves that are rotated about a common axis by combination dials. Each sleeve has a bolt-engaging cam comprising a circular flange with a flat portion. When the dials are placed "on-combination," each cam is in its "unlocked" position, with all the flat portions of the cams aligned to permit the flat bolt to move to an "unlocked" position, so that the lock may be opened. Turning any dial "off-combination" causes the corresponding cam to turn from its unlocked position to a "locked" position at which the circular flange engages the bolt and moves it to a "locked" position, so that the lock may not be opened.
A typical lock of the type disclosed in the Heine patent employs dials with ten discrete combination number positions. To move a dial from one number position to the next requires 36.degree. of dial rotation. Thus, turning a dial from its on-combination position to a succeeding number position in either direction of rotation turns the corresponding cam 36.degree. in either direction from its unlocked position. If the flat portion of the cam subtended 72.degree. (twice 36.degree.), the 36.degree. cam movement just described would cause a point on the circular flange of the cam to contact the bolt tangentially and would produce the same bolt travel regardless of the direction of rotation of the dial from its on-combination position. Unfortunately, if such cams were employed in the typical lock, the amount of bolt travel would be insufficient to ensure reliable cooperation of the bolt with a hasp. In order to achieve additional bolt travel, it has been the practice to employ cams with flat portions that subtend more than 72.degree.. However, this construction has certain disadvantages. First, when a dial is turned in opposite directions from its on-combination position, the bolt travel is not the same. The difference in bolt travel can result in insecure locking. Second, when a dial is one number position away from its on-combination position, the contact of the corresponding cam with the bolt is not tangential. Thus, pressure on the bolt may exert a torque on the cam that moves the cam to its unlocked position. This may occur when the lock is subjected to shock forces, for example.
Sleeves of the type just described are also used in combination locks having a sliding mechanism, rather than a pivoted bolt. For example, U.S. Pat. No. 3,416,338 to Gehrie, issued Dec. 17, 1968, and assigned to the same assignee as the present invention, discloses a combination lock employing a bolt that slides in a direction parallel to the rotational axis of the sleeves. U.S. Pat. No. 3,405,544 to Gehrie, issued Oct. 15, 1968, and assigned to the same assignee as the present invention, discloses a combination lock in which the sleeves slide relative to fixed abutments. U.S. Pat. No. 3,543,545 to Budzyn, issued Dec. 1, 1970, and assigned to the same assignee as the present invention, discloses a combination lock in which a bolt slides in a direction perpendicular to the rotational axis of the sleeves. Such locks also may have problems due to the construction of the sleeves and cooperable parts. For example, as will be discussed in detail later, pressure at the interface of a sleeve and a cooperable part may exert a torque that turns the sleeve to its unlocked position.
It is desirable, therefore, to provide combination locks which overcome the aforesaid difficulties, and it is to this end that the present invention is directed.